This invention pertains to disc type filters and particularly to a disc type filter utilizing a plurality of coaxial superposed rings made arcuate shaped for a more effective filtering and cleaning action.
A disc filter of the counter-current flow cleaning type was described by U.S. Pat. No. 4 430 232, which comprises a series of coaxial ring-shaped filter elements forming a body of a generally cylindrical shape and having between them ring-shaped filtering passages which extend radially from the axis of the filter. In practice however, this filter proved to have the following shortcomings:
When water flows through the filter either during the filtering or the cleaning of the filter, the filter elements vibrate intensely; and the vibration of the filter elements produces an unpleasant noise.
This vibration also produces an abnormal wear of the filter elements, which is due to the abrasion caused by the impurities contained suspended in the liquid and subsequently retained by the filter. This vibration further causes the particulate impurities to desegregation into smaller fragments which cannot be retained by the filter any more. It would be desirable to avoid this desegregation and retain such particulate impurities in the filter. This vibration of the filter elements further produces undesirable changes in the crystalline structure of the weldings, which makes them weak and prone to breaking.
On the other hand however, a vibration of the filter elements ensures advantageously a perfect cleaning of the filter in a very short time, of the order only of several seconds. Furthermore, the filter described in the above-mentioned patent exhibits the following behaviour when it is operated:
When the liquid flows inside the filter at its normal speed, it only passes through the passages between the filter elements of the downstream section of the filter. This phenomenon is of little importance during the filtering, because once the downstream passages are blocked up, the filtering takes place progressively further upstream of the filter body. However, when the filter is subjected to a counter-current flow cleaning, only the downstream section of the filter is actually cleaned, which imposes limitations on the length which can be given to the filter. This problem can be overcome to some extent by placing one or several baffles or deflectors inside the filter, so as to achieve a flow distribution along the filter as uniform as possible. However, this complicates the construction of the filter. Also, the weldings which hold these deflectors on the central shaft of the filter can yield under the vibrations for the same reasons as discussed above.